1. Field of the Invention
The present invention relates to a packaging component and, more particularly, to a part and other elements for use in packaging. The packaging component is useful for the formation of packages having a structure obtained by mounting a semiconductor element or other elements on the packaging component and sealing the element-mounting portion with an insulating resin, and packages in which an adhesive layer is used as a bonding means. The packaging component includes, for example, a lead frame and a heat-radiating or -dissipating plate used in the production of an electronic device. The invention is further relates to a semiconductor package equipped with the packaging component of the present invention and other packages.
2. Description of Related Art
As is well known, there have been proposed a variety of semiconductor packages mounting a semiconductor element such as an IC chip or an LSI chip on a substrate such as a lead frame, and one of them includes a resin-sealed semiconductor package in which a semiconductor element is mounted and a portion mounting the semiconductor element is sealed with an insulating resin. The semiconductor packages as produced are usually stored, and are offered to end users, as required. The end users mount the semiconductor packages on substrates such as wiring boards by reflowing a solder to complete the final electronic devices.
Here, there arises a serious problem of deterioration of adhesion between the lead frame or another packaging component (e.g., heat-radiating plate) in the semiconductor package and the sealing resin. For example, the lead frame is usually made of copper or an alloy thereof and its surface is plated with nickel (Ni) to improve its corrosion resistance and heat resistance. An Ni-plated layer, usually, has a dense and smooth crystalline structure. However, as the Ni-plated layer has a low shearing strength at the interface, good adhesion cannot be maintained between the Ni-plated layer and the sealing resin.
The adhesion between the Ni-plated layer and the sealing resin tends to deteriorate with time. For example, as the semiconductor package is stored until it is mounted on a mounting substrate, the sealing resin can absorb the moisture in the air. As a result, the sealing resin can expand developing defects such as cracks and causing the semiconductor elements to be peeled. Specifically, the moisture absorbed by the sealing resin is rapidly vaporized and expanded due to the heat in the solder reflowing step (a temperature of as high as about 180 to 260° C. is used in this step) at the time of mounting the semiconductor package, producing a large stress in the sealing resin itself. As a result, cracks occur in the interface between the lead frame or the semiconductor element and the sealing resin, and the sealing resin peels off the lead frame. Such defects deteriorate the reliability of the semiconductor package. It has therefore been desired to provide a lead frame or any other packaging component that features excellent adhesion without any deterioration in adhesion.
The above deterioration in adhesion is not limited to the sealing resins only. The adhesive layer is, in many cases, used for bonding the semiconductor element and the packaging component, or between the packaging components. Therefore, the interposed adhesive layer can cause the same problem as in use of the sealing resin.
A keen study has been made in an attempt to solve the above-mentioned problems. For instance, the applicant of this application has invented a metallic insert member such as lead frame which is at least partly embedded in a resin, and in which the surface portion of the insert member embedded in the resin has a rough surface originated from a number of semispherical particles formed by plating (see, Japanese Unexamined Patent Publication (Kokai) No. 6-29439). The insert part is, desirably, a copper lead frame, and the plating, desirably, comprises a copper plating having a rough surface and an Ni plating or an Ni alloy plating formed thereon.
Further, as shown in FIG. 1, there has been proposed a method of forming a black oxide film on the lead frame to reinforce the adhesion to the sealing resin relying upon the anchoring effect (see, Japanese Unexamined Patent Publication (Kokai) No. 9-148509). The lead frame 101 that is illustrated is a press-molded article of copper or a copper alloy, and includes a chip-mounting portion 102, an internal lead portion 103, an external lead portion 104, and a wire-bonding portion 105. Silver layers 102a and 105a are plated on the upper surfaces of the chip-mounting portion 102 and the wire-bonding portion 105. Further, a circuit chip 106 is mounted on the chip-mounting portion 102. The circuit chip 106 and the wire-bonding portion 105 are connected together through a wire 107. Further, the lead frame 101, as a whole, is sealed with a sealing resin 108. In order to reinforce the adhesion between the lead frame 101 and the sealing resin 108 relying upon the anchoring effect, a black oxide film (cupric oxide CuO layer) 109 is formed on the limited portions where the silver layers 102a and 105a have not been plated. The black oxide film 109 is formed by anodizing the lead frame 101 in an organic alkali solution.
However, as modern semiconductor packages are produced in small sizes featuring higher functions, it has been desired to further improve the adhesion between the packaging component such as a lead frame or heat-radiating plate and the sealing resin or the adhesive layer and, at the same time, to prevent deterioration in the adhesion.
In addition to the above-mentioned resin-sealed semiconductor packages, a semiconductor package which has not been entirely covered with the sealing resin causes a new problem. One of the semiconductor packages of this kind is a semiconductor package called QFN (quad flat non-leaded) package. In this semiconductor package, the leads of the lead frame and the die pads are exposed from the surface of the sealing resin. That is, as schematically illustrated in FIG. 2 partly on an enlarged scale, the lead frame includes a conductor substrate 111 of copper and Ni-plated layers 112a and 112b plated on both surfaces thereof, and only the side mounting a semiconductor element (not shown) is covered with the sealing resin 119. Therefore, the Ni-plated layer 112a positioned on the outer side of the semiconductor package is exposed to the outside. Though not illustrated, the semiconductor package equipped with an externally exposed heat-radiating plate, too, is included in this type of semiconductor package.
In these semiconductor packages, portions of the packaging component exposed to the outside are causing a new problem. That is, the exposed portions tend to be scarred or stained while the semiconductor package is being handled, deteriorating the appearance and quality of the product, making the restoration difficult and, further, impairing the laser marking operation. According to the experience of the present inventors, most of the scars are caused by abrasion, scratching and holding, and stains are caused by chemicals and by fingerprints (skin fat), and none of them can be neglected. For reference, the occurrence of scars on the packaging components is described below with reference to FIGS. 3 and 4. Here, in order to confirm the occurrence of scars in the step of cutting after the plating, the reel-like copper lead frame was plated with a rough-surface Ni layer, cut into a sheet size for shipping, and a fixing tape was applied to secure the leads for suppressing dispersion of the leads. The surface state of the Ni-plated layer of the resulting lead frame was observed through a microscope (×50) to confirm a line, considered to be a scar due to abrasion, as illustrated in FIG. 3(A). The scar due to abrasion was further observed on an enlarged scale by using an electron microscope (×2,000) to confirm that the crystals had been crushed on the portion abraded by the metal mold as illustrated in FIG. 3(B). The same lead frame was further observed for its surface state of the Ni-plated layer of another portion using the microscope (×50) to confirm a scar presumably due to holding as illustrated in FIG. 4(A). The pattern of the scar was further observed on an enlarged scale using the electron microscope (×2,000) to confirm that the crystals had been crushed at a portion held by the metal mold as illustrated in FIG. 4(B). In this semiconductor package, too, the Ni-plated layer 112b has a smooth surface without solving the problem of insufficient adhesion between the sealing resin 119 and the Ni-plated layer 112b. 